1.0.3: Multiple updates: Docs, Auth error messages, updated auth strategy.

* migrating changes by @sergey-miryanov (without reformatting code)
  * improved code readability by using common HX and CPP event constants names and values
  * error message for failed Authentication failures.
* updating authenticateLocalUser() to use Apple's current authentication strategy
* adding README to project from Forum and Slack information
* added docs for reportAchievement (Apple uses a 0-100 percentComplete value)